1. Field of the Invention
The present invention relates to a heliostat for collecting sunlight, configured to track the sun and thus to collect reflected light at a desired point (focal point) and also relates to a method of controlling the same. In addition, the present invention relates to a solar thermal power plant configured by using a plurality of the heliostats.
2. Description of Related Art Including Information Disclosed Under 37 CFR §§1.97 and 1.98
In recent years, depletion of petroleum resources and escalation in their prices have been of concern, and a study on shifting to new energy resources from the petroleum resources, which are a cause of global warming, has been conducted. As a new energy source, there is solar thermal power generation, which collects sunlight and uses the sunlight as energy.
FIG. 5 shows an example of a solar thermal power generation apparatus. The solar thermal power generation apparatus includes a heliostat 1X configured to reflect sunlight L from the sun 10 and a heat receiving unit 13 installed at a focal point F of the heliostat 1X. The heliostat 1X includes reflecting mirrors 2X and a support mechanism 3X. This solar thermal power generation apparatus heats a heat medium circulating in the heat receiving unit 13 with the sunlight L collected at the focal point F and generates water vapor or the like by use of the heat of this heat medium, thereby generating power.
The applicant has filed a patent application for a heliostat and a method of controlling the same which generate no comatic aberration for the purpose of improving the power generation efficiency of this solar thermal power generation apparatus (refer to Patent Document 1). This heliostat 1Y includes reflecting mirrors 2Y and a support mechanism 3Y. In addition, this heliostat 1Y includes tilting devices 11. The tilting devices 11 are each configured in such a way that tilt of the tilting device 11 is controlled with rotation angles as the parameters by using link mechanisms 12 in two axial directions. Since this heliostat 1Y tracks the sun 10 by tilting in the two axial directions, it is possible to obtain high light collection efficiency without generating any comatic aberration.
Meanwhile, there is an apparatus configured in such a way that a sun-tracking sensor is installed in each heliostat for the purpose of improving the power generation efficiency (refer to Patent Document 2). With this configuration, the heliostats can form the focal point F on the heat receiving unit 13 with high accuracy.
The heliostat described above has some problems in an aim to further spread solar thermal power generation apparatuses. First, there is a problem that it is difficult to further reduce its manufacturing cost and its installation cost. This is because the number of components of each of the tilting device 11 and the link mechanism 12 is large in particular. For this reason, there is a limitation in reducing the manufacturing cost. In addition, its assembly work requires some time.
Second, there is a problem that improvement in the accuracy in tracking of the sun by the heliostat requires costs. This is because, in consideration of controlling the tilt of the reflecting mirror within an accuracy of ±0.1 degree, an expensive motor is required for tilting the reflecting mirror. In particular, in a case where a reducer is installed in the motor for the purpose of simplifying the control of the heliostat, a minute looseness of a gear causes backlash. The occurrence of such backlash makes it difficult to achieve the aforementioned accuracy within ±0.1 degree with low costs.